Radiotelephony



F. S. McCULLOUGH RADIOTEL'EPHONY.

.APP-LICATION FILED JULY 7.19m.

Lqzmgsz, PatentedSept. 5, 1922'.-

2 SHEETS-SHEET 1.

F. S., Mc'CULLOUGH.

RADIOTELEPHONY.

APPLICATION FILED JULY 7,1919.

m mm m A 5 E4; 4 0 P W W 1h 7 A m m J Patented Sept. 5, 1922.

UNITED STATES PATENT OFFICE.

FREDERICK S. McCULLOfiGH, OF CLEVELAND, OHIO, ASSIGNOR T0 GLENN L.MARTIN,

OF CLEVELAND, OHIO.

BADIOTELEPHONY.

Application med July 7, 1919. Serial No. 308,977.

To all W/umi. it may concern:

Be it known that I, FREDERICK S. MoCUL- LoUon, a citizen of the UnitedStates, resident of Cleveland, county of Cuyahoga, and State of Ohio,have invented new and useful Improvements in Badiotelephony, of whichthe following is a specification, the principle of the invention beingherein explained and the best mode in which I have contemplated applyingthat principle, so as to distinguish it from other inventions.

My invention relates to systems of radio telephony and telegraphy, and,more particularly, to systems for transmitting speech by means ofradiant energy, although it may also be applied to other purposes.

The object of my invention is to provide uniform and regular electricoscillations with small damping and having abundant power, and moreover,to furnish these oscillations by means of a simple, compact, economicaland continuously reliable apparatus which operates with freedom frominherent vibrations of audible frequency, and is therefore especiallyapplicable to radio telephony, although it may also be used for anyother form of radio transmission.

Among the means hitherto employedto supply undamped oscillations forradio telephony, are high-frequency spark gaps and vacuum tubes.Considerable amounts of power can be employed with the spark gaps, butthe oscillations produced are irregular, and introduce noises and soundswhich interfere very greatly with satisfactory speech. The vacuum tubesproduce smooth and regular oscillations, but are limited in power.Higlrtrequency alternating-current machines are also used to produceoscillations for radio work, but are unsuitable where space and weightmust be limited.

The present invention provides a means to make use of the spark gap, andat the same time to eliminate its objectionable features. The means Iemploy is an are contained in a sealed tube filled with an inert gas,such as argon, but is not limited to any particular gas. This are isplaced in series with'the high-frequency spark gap and acts as astabilizer or filter or buifer or equalizer for the irregularoscillations emanating from the spark gap. In this way high-frequencyoscillations of great power and yet of smooth and regular form areproduced, and can be used for any kind of radio transmisslon.

This system is particularly applicable to radio telephony, and for suchpurposes it possesses an additional feature which is of great value inmodulating the power current by means of the sound waves. Thisadditional feature consists of a third electrode in the tube containingthe are, placed in the path of the are, between the anode and thecathode, and in circuit with the microphone transmitter and battery.

Other advantages of my invention will appear from the furtherdescription, reference being made to the drawings accompanying thisspecification.

The annexed drawings and the following description set forth in detailcertain means embodying my invention, the disclosed means, however,constituting but one of the various mechanical forms in which theprinciple of the invention may be applied.

In said annexed drawings:

Figure 1 is a diagrammatic representation, showing one arrangement of mycircuits and a View of one form of my arc st abilizer.

Figure 2 is a diagram of another arrangement of circuits with a modifiedform of my stabilizing are having a third electrode.

Figure 3 shows a third arrangement of circuits and a third form of mystabilizing arc, the third electrode being in the form of a filament.

Figure 4; shows a fourth arrangement of circuits, with the same form ofstabilizing are as shown in Figure 3.

In Figure 1, 1 is a generator; 2, 2, are impedances; 3 is a variableresistance; 4 is a condenser; 5 is a high-frequency spark gap; 6 is asealedvessel containing an inert gas, an anode 7 and a cathode 8,between which my stabilizing are is formed; and 18 is a variablecondenser. 1 9 is the primary of an oscillation transformer, thesecondary of which, 10, is a variable inductance, in circuit with theantenna 11, the ammeter 12 and the ground 13. 14 is a microphone forimpressing modulations of audible frequency on the antenna circuit. 16is a switch for shortcircuiting the microphone when it is desired tosend telegraph signals by means of the key 15. 17 is a switch which isclosed when the microphone is used, and open when the key 15 is beingoperated.

In Figure 2, 1 is a generator, 2, 2 are impedances, 3 is a variableresistance, 4 is a condenser, 5 is a highrfrequency spark (gap, 6 is asealed vessel, in which are an ano e 7 a cathode 8, and a thirdelectrode 20; the anode and cathode being in the power circuit with thespark gap, and the third, electrode being in the modulating circuit withthe microphone. 9 is the primary of an oscillation transformer, thesecondary of which, 10, is in circuit with the antenna 11, the ammeter12, and the ground 13. 14 is a microphone; 15 is a telegraph key; 16 isa switch for shortcir'cuitingthe microphone; 18 is a variable condenserabout the stabilizing arc inthe sealed vessel 6; 19 is a variablecondenser. 21 is an inductance coil in circuit with the microphone andthe electrode 20, and in inductive relation to the secondary, 10, of theoscillation transformer, and 22-is a battery in the modulating circuit.

In Figure 3, 1 is a generator; 2 is an impedance; 3 is a variableresistance; 4 is a condenser; 5 is a spark gap; 6 is a sealed vesselcontaining an anode 7, a cathode 8, and a third electrode 23 in the formof a filament which can be heated by an external source; 9 is theprimary of an oscillation transformer, the secondary of which, 10, is incircuit with the antenna 11, the ammeter 12 and the ground 13. 14 is amicrophone; 15 is a telegraph key; 16 is a switch for shortcircuitingthe microphone; 19 is a condenser in the modulating circuit whichcontains the microphone and the filament 23. 24- is a battery which isused for heating the filament and which also may supply current for themodulating circuit. 25 is a variable resistance for regulating theheating current through the filament, and 26 is a potentiometerresistance for adjusting the potential offilament 23 with respect to theoathode 8, thus regulating the current in the modulating circuit. Thevariable resistance 26 has a resistance of several thousand ohms, sothat very little of the current from the battery 24 passes through it,and its principal function is that of a potentiometer. 27 is aswitch and28 and 29 are contacts. When the microphone is in use, the switch shouldbe in the position as shown, making contact with 28. When the telegraphkey 15 is to be used, however, the switch should be thrown so as to makecont-act with 29. 30 is a variable condenser about the sealed vessel 6and the coil 9.

In Figure 4, 1 is a generator, 2 is an impedance, 3 is a variableresistance; 4 is a condenser; 35 is a spark gap of any suitable kind; 6is a sealed vessel having an anode 7, a cathode 8, and a third electrode23 in the form of a filament. 9 is the primary of an oscillationtransformer, the secondary of which, 10, is in circuit with the antenna11, the ammeter 12 and the ground 13. 15 is a telegraph key; 17 is aswitch which is closed when the key is not in operation, and open.

when it is desired to send telegraph signals. 2 1 is a battery; 25 is avariable resistance. 27 is a switch having contacts 28 and 29. 30 is avariable condenser about the sealed vessel 6, 31 is a battery in themodulating circuit; 32 is a microphone; 33 is a microphone battery, and34 is a transformer.

As shown in the drawings, the power circuit comprises the generator, thespark gap and the stabilizing arc, together with other features. Thegenerator 1 is of relatively high voltage; the current from thisgenerator is controlled by the impedances 2 and the resistance 3 andcharges the condenser 4:, which discharges across the spark gap 5. Thisgap may be of any suitable kind, as shown in Figure 4:, but ispreferablycomposed of dissimilar metals of such a character and so disposed thatwhen the apparatus is active, a much larger discharge current passesacross the gap in one direction than in the opposite direction, as shownin the other figures. I have employed metals such as copper andaluminum, and other metals which will also be effective have been used,or a mixture of alloys of two metals will also produce similar effects.

IVhen this gap operates by itself, as in previous systems, it producesoscillations of high frequency. but of more or less irregularity, as canbe easily observed by listening in with an appropriate receiving device,when there are heard hissing and scratching noises often loud enough toobliterate articulate speech. In order to overcome this difficulty, Iinvented and developed my arc stabilizer modulating tube. This tubecontains electrodes composed of dissimilar metals. The cathode. forinstance. is of tungsten, and it has been found most advantageous to useit in the shape of a coil. The anode is preferably composed of a disk ofgraphite. In the preferred form of my invention, there is also placedbetween the anode and the cathode, a third electrode, preferablycomposed of tungsten, which acts as-the controlling member of themodulating circuit.

In preparing the tube, the space within it should be carefully evacuatedof all gases and vapor, and particular care should be taken to removeelectro-negative gases, or gases which will, at high temperatures, yieldelectro-negative gases. for example, water vapor. After the tube iscarefully evacuated, it is then filled with an inert gas, such as argon,although it is not limited to any particular gas.

The operation of this are within the sealed vessel is probably asfollows: When the discharge takes place across the gap 5, the initialresistance of the tube 6 is broken down, a flow of current takes placethrough the tube, and an arc is established between the'electrodes. Theeffect produced by this are tabilizer modulating tube is such that thespark-gap oscillations, which were previously of a varying amplitude,are now regulated so that they are of constant amplitude and smoothform, and all disturbing noises are eliminated. This arc stabilizer tubecan carry heavy currents and is generally designed for comparatively lowvoltages. I have operated it with currents of eight (8) amperes, atthirty-five volts, but I do not limit myself to any particular currentsor voltages.

I/Vhen voice modulations are impressed upon the power circuit,therefore, thereis no interference with the speech vibrations. Acondenser may be shunted across the anode and cathode of the tube, toincrease the current in thepower circuit.

In Figure 1, the voice modulations are impressed upon the antennacircuit by a microphone, and there is also connected with this circuit atelegraph key, by means of which signals can be sent. In the preferredforms of my invention, shown in the other figures, the voice modulationsand the telegraph signals are impressed upon the power circuit by meansof a control member which consists of a third'electrode in the sealedtube or vessel, placed between the anode and the cathode of the arc. Thepotential of the control member or element is preferably 'made negativewith respect to. the cathode element, so that when the microphone isspoken into, the current in the power circuit drops to zero, whichproduces exceptionally good articulation. The control member may becharged negatively by a battery such as shown at 22, Figure 2.

The oscillation transformer 9, 10, for transferring the oscillations ofthe power circuit to the antenna circuit, comprises a primary, 9,loosely coupled to the secondary, 10. In the form of my system shown inFigure 2, the coil, 21, in the controlling or modulating circuit iswound tightly upon the secondary of the oscillation transformer,providing a loose coupling to the secondary 10. This arrangement enablesme to increase the spark frequency in the power circuit. But thisauxiliary coil may be dispensed with in some forms of my system.

In Figure 2, the control member, 20, is shown as an electrode in thesealed vessel, and it may have any suitable form, such, for instance, asa wire wound in a flat spiral. I find that under some circumstances, Iam able to improve the operation of my system,

In forms of my system where the third electrode is not preheated, Isometimes preheat the cathode by making it inthe form of a filament andheating it by a source external to the tube, such as a battery. Thispreheating of the cathode assists in starting the are quickly, and hasother advantages.

I have found that by inserting my arc stabilizer tube, the efficiency ofthe system is greatly increased. For example, without the tube, thecurrent in the power circuit is three and one-half (3J amperes, and thecurrent in the antenna circuit isone and onehalf (1%) amperes. Oninserting the tube, the current in the power circuit drops to aboutthree (3) amperes, while the current in the antenna circuit rises to twoand one half (29;) amperes. This improvement is probably due to theincreased smoothness and regularity of the oscillations and theiruniform amplitude owing to the action of the stabilizing arc.

I do not confine myself to the exact constructions and arrangementsherein described, but may also employ other means well known to thoseskilled in the art, but what I claim and desire to secure by LettersPatent is:

1. In a system of radio telephony, a power circuit including ahigh-frequency spark gap and an electric are having an anode and acathode, and a modulating circuit including a microphone and a thirdelectrode associated with said are, said third electrode consisting ofafilament heated by a source external to the arc.

'2. In a system of radio transmission, a power circuit including a sparkgap, an electric arc and an inductance coil, an antenna circuitincluding an inductance coil in mductive relation to said inductancecoil in the power circuit, and a modulating circuit including amicrophone transmitter and an inductance coil in inductive relation tosaid inductance coil in the antenna circuit. I

Signed by me, this 26th day of June, 1919.

F, S. MQCULLOUGH.

